JP6859799B2 - Paste-like silver powder composition, method for producing a bonded body, and method for producing a silver film - Google Patents

Description

The present invention relates to a paste-like silver powder composition, a method for producing a conjugate using the paste-like silver powder composition, and a method for producing a silver film.

It is known that a fine metal powder composed of metal nanoparticles having a nano-sized particle size can be sintered at a temperature lower than the original melting point of the metal. In particular, since silver powder has high conductivity and heat dissipation, a paste-like silver powder composition in which fine silver powder is dispersed in a solvent is a bonding material for bonding a circuit board and electronic components such as semiconductor chips and LED elements. It is attracting attention as a raw material for electrodes of solar cell elements.

For example, Patent Document 1 states that silver fine particles coated with an organic compound having 8 or less carbon atoms such as hexanoic acid and having an average primary particle diameter of 1 to 50 nm and silver fine particles coated with an organic compound such as oleic acid have an average primary particle diameter of 0. A paste-like silver powder composition containing 5 to 4 μm silver particles, a solvent composed of a primary alcohol solvent and a terpene alcohol solvent, and a dispersant composed of a phosphoric acid ester dispersant is disclosed.

Japanese Unexamined Patent Publication No. 2015-225842

With the recent miniaturization and higher functionality of electric devices, the integration of semiconductor elements is increasing, and the amount of heat generated by the semiconductor elements tends to increase. Therefore, in the paste-like silver powder composition, it is desired that a dense silver film (silver powder sintered body) having few pores can be formed in a fine pattern by heating at a low temperature as much as possible. By forming a dense silver film, the substrate circuit and the semiconductor element can be bonded with high bonding strength, and since the thermal conductivity is high, the heat generated by the semiconductor element can be easily released to the outside, and further. Has the advantage that it is less likely to be damaged by thermal expansion or contraction.

Conventionally, in order to make it possible to form a dense silver film, it has been studied to increase the concentration of silver powder in the paste-like silver powder composition. However, when the concentration of silver powder in the paste-like silver powder composition is increased, the viscosity is increased and the coatability is lowered, which may make it difficult to form a silver film in a fine pattern. Further, as described in Patent Document 1, it has been studied to add a dispersant in order to reduce the viscosity of the paste-like silver powder composition. However, the addition of the dispersant hinders the sintering of silver powder during heating, and the density of the obtained silver film is rather low, which may reduce heat dissipation and bondability.

The present invention has been made in view of the above circumstances, and can form a silver film (silver powder sintered body) having excellent coatability and high heat dissipation and bondability by heating at a relatively low temperature. It is an object of the present invention to provide a paste-like silver powder composition. The present invention also includes a method for producing a bonded body capable of producing a bonded body having high thermal conductivity and bonding strength by heating at a relatively low temperature, and a silver film having high thermal conductivity by heating at a relatively low temperature. It is also an object of the present invention to provide a method for producing a silver film capable of producing the same.

In order to solve the above problems, the paste-like silver powder composition of the present invention is selected from at least a group consisting of silver powder, a polymer dispersant having an amino group or a formic acid group, and diols and carbitol acetates. The silver powder contains one kind of solvent, and the silver powder contains one or more kinds of carboxylic acids selected from the group consisting of glycolic acid, ammonium citrate and malonic acid or salts thereof, and hydrazine, formic acid, ammonium formate and ascorbin. organic compounds derived from the one or more reducing agents selected from the group consisting of sodium is adhered to the surface, as measured by time-of-flight secondary ion mass spectrometry, the organic compound derived from C ₃ H ₃ O ₃ ^- detection of ions is, the detection of Ag ⁺ ions, 0. In the range of 1.0 times more than doubled, and the C ₆ H ₆ O ₈ derived from organic compounds ^- detecting the amount of ions, the detection amount of the Ag ⁺ ion, 0.005 times 0 The polymer dispersant is in the range of .02 times or less, the peak top molecular weight measured by gel filtration chromatography is in the range of 1500 or more and 15,000 or less, and the content of the polymer dispersant is 1% by mass. It is characterized in that it is in the range of 5% by mass or less.

In pasty silver powder compositions of this configuration, silver powder, C ₃ H ₃ O ₃ by time-of-flight secondary ion mass spectrometry ^- it is coated with an organic compound to be detected as an ion ^- ion and C ₆ H ₆ O ₈ Therefore, aggregation of silver particles is suppressed, and the coatability of the paste-like silver powder composition is improved. Then, the respective detection amounts of _{C 3} H ₃ O ₃ ⁻ ion and C ₆ H ₆ O ₈ ⁻ ion measured by this time-of-flight secondary ion mass spectrometry are relative to ^{the detection amount of Ag +} ion. , _{C 3 H} 3 _O 3 ^- ions of the detection amount is 0.2 times to 1.0 times or less, and _C 6 _H 6 _{O 8} ^- the range detection amount less 0.02 times 0.005 times the ion Since the amount of the organic compound covering the particle surface is small, the organic compound disappears and the surface of the silver particle is exposed by heating at a relatively low temperature, so that the silver particles are sintered at a relatively low temperature. It is possible to make it.

Further, in the paste-like silver powder composition having the above-mentioned structure, the polymer dispersant having a nitrogen atom or a phosphorus atom in the molecule adheres to the surface of the silver particles, so that aggregation of the silver particles is suppressed and the paste-like silver powder composition is formed. The coatability of the silver powder composition is improved. Further, since the polymer dispersant has a peak top molecular weight of 1500 or more as measured by gel filtration chromatography, aggregation of silver particles is reliably suppressed. Further, since the polymer dispersant has a peak top molecular weight of 15,000 or less, it is easily desorbed from the surface of silver particles when heated, and silver particles can be sintered at a relatively low temperature.

As described above, in the paste-like silver powder composition having the above structure, the aggregation of the silver particles is suppressed by combining the organic compound that coats the surface of the silver particles and the polymer dispersant. Therefore, even if the content of the polymer dispersant is in a range of 1% by mass or more and 5% by mass or less, which is a relatively small amount, the coatability of the paste-like silver powder composition can be improved. Since the content of the polymer dispersant is as small as 5% by mass or less, the silver particles can be sintered by heating at a relatively low temperature. Therefore, a silver film having high heat dissipation and bondability can be obtained by heating at a relatively low temperature.

Furthermore, since the paste-like silver powder composition having the above structure contains at least one solvent selected from the group consisting of diols and carbitol acetates, the coatability is further improved.

Here, in the pasty silver powder composition of the present invention, the polymer dispersant, Ru polymer dispersant der having an amino group or a phosphoric group. That is, the nitrogen atom in the molecule as an amino group, a phosphorus atom is that present as a phosphate group.
In this case, the polymer dispersant can be more reliably adhered to the surface of the silver particles, whereby the coatability of the paste-like silver powder composition can be further improved.

Further, in the paste-like silver powder composition of the present invention, the solvent is preferably ethylene glycol, 2-ethyl-1,3-hexanediol or butyl carbitol acetate.
In this case, the coatability of the paste-like silver powder composition is surely improved.

The method for manufacturing a bonded body of the present invention is a method for manufacturing a bonded body in which a first member and a second member are joined via a bonding layer, and the first member and the second member In a laminating step of forming a laminated body laminated via the paste-like silver powder composition of the present invention, and by heating the laminated body, the paste-like silver powder composition is dried and sintered to form a bonded layer. It is characterized by having a sintering process for producing.

According to the method for producing a bonded body having this configuration, since the above-mentioned paste-like silver powder composition is used as a bonding material for forming a bonding layer, a bonded body having high thermal conductivity and bonding strength can be produced by heating at a relatively low temperature. can do.

The method for producing a silver film of the present invention comprises a coating step of applying the paste-like silver powder composition of the present invention to a base material and heating the base material coated with the paste-like silver powder composition to form the paste. It is characterized by including a sintering step of drying and sintering the silver powder composition to form a silver film.

According to the method for producing a silver film having this structure, since the above-mentioned paste-like silver powder composition is used as the material for the silver film, a silver film having high thermal conductivity can be produced by heating at a relatively low temperature.

According to the present invention, it is possible to provide a paste-like silver powder composition which is excellent in coatability and can form a silver film (silver powder sintered body) having high heat dissipation and bondability by heating at a relatively low temperature. It becomes. Further, according to the present invention, a method for producing a bonded body capable of producing a bonded body having high thermal conductivity and bonding strength by heating at a relatively low temperature and silver having high thermal conductivity by heating at a relatively low temperature. It becomes possible to provide a method for producing a silver film capable of producing a film.

It is sectional drawing of the bonded body manufactured by using the manufacturing method of the bonded body of this embodiment.

Hereinafter, a paste-like silver powder composition, a method for producing a conjugate, and a method for producing a silver film, which are embodiments to which the present invention is applied, will be described in detail. In addition, in the drawings used in the following description, in order to make the features easy to understand, the featured parts may be enlarged for convenience, and the dimensional ratios of each component may not be the same as the actual ones. Absent.

<Paste-like silver powder composition>
The paste-like silver powder composition of the present embodiment contains silver powder, a polymer dispersant, and a solvent. Hereinafter, each of these components will be described.

(Silver powder)
The silver powder used in this embodiment is made of pure silver and a silver alloy containing silver as a main component (silver content of 99% by mass or more). The average particle size of the silver powder is 100 nm or more and 150 nm or less in nano size. By using silver powder containing silver with high purity and having an average particle size of nano size, by heating at a temperature lower than the original melting point of silver, for example, 130 ° C. or higher, preferably 150 ° C. or higher. , It becomes possible to sinter silver powder.

In the silver powder used in this embodiment, the detection amounts of _{C 3} H ₃ O ₃ ⁻ ions and C ₆ H ₆ O ₈ ⁻ ions in the time-of-flight secondary ion mass spectrometry (TOF-SIMS) ^{are Ag +.} the detection of the ^{_{ion, C 3 H 3 O 3 -}} 1.0 times the detected amount of 0.2 times or more of the ions less, and _C 6 _H 6 _{O 8} ^- detection of ions 0.005 times 0 The range is 0.02 times or less.

Flying is detected in time-SIMS C ₃ H ₃ O ₃ ^- ions and C ₆ H ₆ O ₈ ^- ions are derived from an organic compound coating the silver particles surface (protecting agent).
C ₃ H ₃ O ₃ ^- ions and C ₆ H ₆ O ₈ ^- the detection of ions is too small, i.e. the surface activity of the amount is small becomes excessively when silver particles of the organic compound coating the silver particle surface As a result, the silver particles tend to aggregate, the viscosity of the paste-like silver powder composition may increase, and the coatability may decrease. On the other hand, C ₃ H ₃ O ₃ ^- ions and C ₆ H ₆ O ₈ ^- the detection of the ion is too high, i.e. the amount of the organic compound coating the silver particle surface is too large, sinterability It may be necessary to raise the heating temperature for sintering the silver powder.

For these reasons, in the present embodiment, the detection amount of Ag ⁺ _ions, C ₃ H _{3 O 3} ^- detection of ions 0.2 times to 1.0 times or less, and _C 6 _H 6 _{O 8} ^- detection of ions is in the range of less than 0.02 times 0.005 times. Note that reliably improves the storage stability of the silver powder, in order to reliably reduce the sintering temperature, C ₃ H ₃ O ₃ for detecting the amount of Ag ⁺ ions ^- detection of the ion is 0.3 times or more 0 It is preferably 0.5 times or less. Further, it is preferable that the organic compound adhering to the surface of the silver particles has a low molecular weight because it is easily eliminated by heating. _Thus, C ₃ H _{3 O 3} ^- detection of _ions, C ₆ H _{6 O 8} ^- it is preferably larger than the detected amount of ions. C ₃ H ₃ O ₃ ^- detection of _ions, C ₆ H _{6 O 8} ^- is preferably in the range of 30 times 50 times or less with respect to the detection of ions.

The shape of the silver particles of the silver powder is not particularly limited, and specific examples thereof include a spherical shape, a rod shape, and a scale shape.

The content of silver powder in the paste-like silver powder composition is, for example, in the range of 75% by mass or more and 95% by mass or less. If the content of silver powder is too low, it may be difficult to form a high-density silver film. On the other hand, if the content of the silver powder becomes too large, the viscosity of the paste-like silver powder composition may increase and the coatability may decrease.

For the above silver powder, for example, a silver salt aqueous solution and a carboxylic acid aqueous solution in which a carboxylic acid or a carboxylic acid salt is dissolved are simultaneously added dropwise to water to generate silver carboxylate particles to prepare a silver carboxylate slurry. One step, a second step of preparing a silver powder slurry by dropping an aqueous solution of a reducing agent onto a silver carboxylate slurry and heat-treating the obtained mixed slurry to reduce silver carboxylate particles to generate silver particles. It can be produced by a method having a third step of recovering silver powder from the silver powder slurry.

In the first step, since the silver salt aqueous solution and the carboxylic acid aqueous solution are simultaneously added dropwise to the water, the silver salt concentration and the carboxylic acid salt concentration in the water are lowered. Therefore, the silver salt concentration and the reaction rate of the carboxylate become slow, and fine silver carboxylate particles having a nano-sized particle size are produced.

The ratio of the amounts of the silver salt aqueous solution and the carboxylic acid aqueous solution to be dropped into water at the same time is the equivalent ratio of silver and carboxylic acid [= (silver ion valence: 1 valence x molar number) / (carboxylic acid valence x molar number). )], It is preferable that the range is 1.1 or more and 2.0 or less. In this case, as the dropping progresses, the amount of free carboxylic acid in the water increases, so that the time from dropping the silver salt aqueous solution to the formation of silver carboxylic acid particles is shortened, so that fine carboxylic acid is formed. Silver acid particles are easily generated.

Here, when preparing the silver carboxylate slurry, it is preferable to keep the temperature of each of the silver salt aqueous solution, the carboxylic acid aqueous solution and the water (silver carboxylate slurry) at a predetermined temperature within the range of 20 to 50 ° C. .. By keeping the temperature of each liquid at a predetermined temperature of 20 ° C. or higher, silver carboxylate particles can be easily generated, and the particle size of the silver carboxylate particles can be increased. Further, by keeping the temperature of each liquid at a predetermined temperature of 50 ° C. or lower, it is possible to prevent the silver carboxylate particles from excessively growing to become coarse particles.

Further, it is preferable that the water is stirred while the silver salt aqueous solution and the carboxylic acid aqueous solution are simultaneously added dropwise to the water.

As the silver salt aqueous solution, an aqueous solution of one or more silver salt compounds selected from the group consisting of silver nitrate, silver chlorate and silver phosphate can be used.

As the aqueous solution of carboxylic acids, an aqueous solution of one or more carboxylic acids selected from the group consisting of glycolic acid, citric acid, malic acid, maleic acid, malonic acid, fumaric acid, succinic acid and tartaric acid or salts thereof. Can be used. Since these carboxylic acids form a stable chelate with silver, they are likely to precipitate as silver carboxylate particles. The carboxylic acid salt is preferably an ammonium salt or an alkali metal salt of these carboxylic acids.

As the water, ion-exchanged water and distilled water can be used. It is particularly preferable to use ion-exchanged water because it does not contain ions that may adversely affect the formation of silver carboxylate particles and its production cost is lower than that of distilled water.

In the second step, it is preferable to perform a heat treatment in which the mixed slurry obtained by dropping the reducing agent aqueous solution onto the silver carboxylate slurry is held at a temperature in the range of 92 ° C. or higher and 95 ° C. or lower. By setting the holding temperature of the mixed slurry to 92 ° C. or higher, silver carboxylate is easily reduced, and silver particles can be rapidly generated. Further, by setting the holding temperature of the mixed slurry to 95 ° C. or lower, the carboxylic acid can be attached to _{the surface of the generated silver particles as C 3} H ₃ O ₃ ⁻ ions or C ₆ H ₆ O ₈ ^{− ions.} Therefore, it is possible to prevent the silver particles from becoming coarse particles.

The time for holding the mixed slurry at the above temperature is preferably in the range of 0.25 to 0.5 hours. By setting the holding time to 0.25 hours or more, silver carboxylate can be reliably reduced, and silver particles can be stably produced. Further, by setting the holding time to 0.5 hours or less, it is possible to prevent the generated silver particles from becoming coarse particles.

As one method of setting the mixed slurry to the above temperature, a method of preparing the mixed slurry at a temperature of less than 92 ° C. and then heating the mixed slurry can be mentioned. In this method, it is preferable to set the heating rate of the mixed slurry in the range of 15 to 20 ° C./hour. By increasing the heating rate to 15 ° C./hour or more, it is possible to prevent the silver particles from becoming coarse particles. By setting the temperature to 20 ° C./hour or less, unevenness is less likely to occur in the liquid temperature inside the mixed slurry.

Another method of adjusting the mixed slurry to the above temperature is to heat the silver carboxylate slurry and the aqueous reducing agent solution to maintain the liquid temperature within the range of 92 or more and 95 ° C. or less, and silver carboxylate. A method of dropping an aqueous reducing agent solution onto the slurry can be mentioned. In this method, the liquid temperature inside the mixed slurry is less likely to be uneven.
be able to.

As the reducing agent aqueous solution, an aqueous solution of one or more compounds selected from the group consisting of hydrazine, ascorbic acid, oxalic acid, formic acid, and salts thereof can be used.

The prepared silver powder slurry is preferably cooled quickly in order to prevent the silver particles from becoming coarse particles. The silver powder slurry is preferably cooled at a temperature lowering rate such that the time for lowering the temperature to 30 ° C. is 15 minutes or less.

In the third step, silver powder is recovered from the silver powder slurry. As a method for recovering the silver powder, a method of drying the silver powder slurry can be used. Before drying the silver powder slurry, it is preferable to remove the liquid layer in the silver powder slurry using a centrifuge to dehydrate and desalt the silver powder slurry.

The method for drying the silver powder slurry is not particularly limited, and specific examples thereof include a freeze-drying method, a vacuum drying method, and a heat-drying method. The freeze-drying method is a method in which silver powder slurry is placed in a closed container and frozen, the inside of the closed container is depressurized with a vacuum pump to lower the boiling point of the object to be dried, and the moisture of the object to be dried is sublimated and dried at a low temperature. is there. The vacuum drying method is a method of drying the object to be dried under reduced pressure. The heat-drying method is a method of heating to dry an object to be dried.

(Polymer dispersant)
The polymer dispersant used in this embodiment has a nitrogen atom or a phosphorus atom in the molecule. The molecular weight of the polymer dispersant is in the range of 1500 or more and 15000 or less as the peak top molecular weight measured by gel filtration chromatography. In this embodiment, the nitrogen atom in the molecule exists as an amino group and the phosphorus atom exists as a phosphoric acid group. In this case, it is considered that the polymer dispersant is attached to the organic substance covering the surface of the silver particles via an amino group or a phosphoric acid group. By adhering the polymer dispersant to the surface of the silver particles, aggregation of the silver particles is suppressed, and the coatability of the paste-like silver powder composition is improved. Further, the amino group or the phosphoric acid group is easily desorbed from the surface of the silver particles by heating at a relatively low temperature. Therefore, it is possible to sinter the silver particles by heating at a relatively low temperature.

If the peak top molecular weight of the polymer dispersant becomes too small, the effect of suppressing the aggregation of silver particles becomes weak, the silver particles aggregate, the viscosity of the paste-like silver powder composition increases, and the paste-like silver powder composition May reduce the applicability of. On the other hand, if the peak top molecular weight of the polymer dispersant becomes too large, it becomes difficult for the polymer dispersant to desorb from the surface of the silver particles during heating, and the heat dissipation and bondability of the obtained silver film may deteriorate. Therefore, in the present embodiment, the peak top molecular weight of the polymer dispersant is set in the range of 1500 or more and 15000 or less.

The position of the amino group or the phosphoric acid group of the polymer dispersant is not particularly limited and may be in the main chain or the side chain. It may also be in the main chain and the side chain, respectively. Further, the polymer dispersant may have an amino group and a phosphoric acid group.

The content of the polymer dispersant is in the range of 1% by mass or more and 5% by mass or less. If the content of the polymer dispersant is too small, the effect of suppressing aggregation of silver particles is weakened, and the coatability of the paste-like silver powder composition may be lowered. On the other hand, if the content of the polymer dispersant is too large, the amount of the polymer dispersant remaining on the surface of the silver particles during heating increases, and the heat dissipation and bondability of the obtained silver film may deteriorate. ..

(solvent)
The paste-like silver powder composition of the present embodiment contains at least one selected from the group consisting of diols and carbitol acetates as a solvent.
The diols are preferably chain hydrocarbon diols. The chain hydrocarbon diol may have a branch. Examples of diols include ethylene glycol, diethylene glycol, polyethylene glycol, and 2-ethyl-1,3-hexanediol. Examples of carbitol acetates include butyl carbitol acetate and ethyl carbitol acetate. These solvents may be used alone or in combination of two or more. The solvent is preferably ethylene glycol, 2-ethyl-1,3-hexanediol or butylcarbitol acetate.

The content of the solvent is in the range of 1% by mass or more and 20% by mass or less. If the content of the solvent is too small, the viscosity of the paste-like silver powder composition may increase, and the coatability may decrease. On the other hand, if the solvent content is too high, the silver powder content is relatively low, which may make it difficult to form a dense silver film.

The paste-like silver powder composition preferably has a viscosity of 50 Pa · s or less, and more preferably 15 Pa · s or more and 40 Pa · s or less. The viscosity of the paste-like silver powder composition can be measured using a rheometer.

(Manufacturing method of paste-like silver powder composition)
The paste-like silver powder composition of the present embodiment can be produced by kneading the above-mentioned silver powder, the polymer dispersant, and the solvent at a mixing ratio having the above-mentioned contents. The kneading method is not particularly limited, and can be carried out using various kneading machines used in the production of a conventional paste-like silver powder composition.

In the paste-like silver powder composition of the present embodiment having the above-mentioned structure, the silver powder is C ₃ H ₃ O ₃ ⁻ ions and C ₆ H ₆ O ₈ ⁻ ions by time-of-flight secondary ion mass spectrometry. Since it is coated with the organic compound detected as, the aggregation of silver particles is suppressed, and the coatability of the paste-like silver powder composition is improved. Then, the respective detection amounts of _{C 3} H ₃ O ₃ ⁻ ion and C ₆ H ₆ O ₈ ⁻ ion measured by this time-of-flight secondary ion mass spectrometry are relative to ^{the detection amount of Ag +} ion. , _{C 3 H} 3 _O 3 ^- ions of the detection amount is 0.2 times to 1.0 times or less, and _C 6 _H 6 _{O 8} ^- the range detection amount less 0.02 times 0.005 times the ion Since the amount of the organic compound covering the particle surface is small, the organic compound disappears and the surface of the silver particle is exposed by heating at a relatively low temperature, so that the silver particles are sintered at a relatively low temperature. It is possible to make it.

Further, in the paste-like silver powder composition of the present embodiment, the polymer dispersant having a nitrogen atom or a phosphorus atom in the molecule adheres to the surface of the silver particles, so that aggregation of the silver particles is suppressed and the paste-like silver powder composition is formed. The coatability of the silver powder composition is improved. Further, since the polymer dispersant has a peak top molecular weight of 1500 or more as measured by gel filtration chromatography, aggregation of silver particles is reliably suppressed. Further, since the polymer dispersant has a peak top molecular weight of 15,000 or less, it is easily desorbed from the surface of silver particles when heated, and silver particles can be sintered at a relatively low temperature.

As described above, in the paste-like silver powder composition of the present embodiment, the aggregation of the silver particles is suppressed by combining the organic compound that coats the surface of the silver particles and the polymer dispersant. Therefore, even if the content of the polymer dispersant is in a range of 1% by mass or more and 5% by mass or less, which is a relatively small amount, the coatability of the paste-like silver powder composition can be improved. Since the content of the polymer dispersant is as small as 5% by mass or less, the silver particles can be sintered by heating at a relatively low temperature. Therefore, a silver film having high heat dissipation and bondability can be obtained by heating at a relatively low temperature.

Furthermore, since the paste-like silver powder composition having the constitution of the present embodiment contains at least one solvent selected from the group consisting of diols and carbitol acetates, the coatability is further improved.

Further, in the paste-like silver powder composition of the present embodiment, it is preferable that the nitrogen atom in the molecule is present as an amino group and the phosphorus atom is present as a phosphoric acid group in the polymer dispersant. It can be more reliably adhered to the surface of the silver particles, whereby the coatability of the paste-like silver powder composition can be further improved.

The paste-like silver powder composition of the present embodiment may further contain additives such as an antioxidant, a viscosity modifier, and a surfactant depending on the intended use. These additives may be used alone or in combination of two or more.

<Manufacturing method of joint>
Next, a method for manufacturing the bonded body of the present embodiment will be described with reference to FIG.
FIG. 1 is a cross-sectional view of a joined body manufactured by using the method for manufacturing a joined body of the present embodiment. In FIG. 1, the bonded body 11 is roughly configured by including a substrate 12, a first metal layer 13, a bonded layer 14, a second metal layer 15, and an object to be joined 16.

In the present embodiment, as an example, the bonded body 11 in which the substrate 12 (first member) and the object to be bonded 16 (second member) are bonded to each other using the paste-like silver powder composition described above will be described. The material to be bonded using the silver powder composition is not particularly limited.

The substrate 12 is not particularly limited, and specific examples thereof include an aluminum plate and an insulating substrate to which an aluminum plate is bonded.

The first metal layer 13 is laminated adjacent to the substrate 12. The substrate 12 and the bonding layer 14 are bonded via the first metal layer 13. As the material of the first metal layer 13, for example, one kind or two or more kinds of metals selected from the group consisting of gold, silver, copper and the like can be used.

The bonding layer 14 is laminated adjacently between the first metal layer 13 and the second metal layer 15.
The bonding layer 14 is in contact with the first metal layer 13 to form an interface 17. Further, the bonding layer 14 is in contact with the second metal layer 15 to form an interface 18. The bonding layer 14 is formed by applying the above-mentioned paste-like silver powder composition on the first metal layer 13, placing the object to be bonded 16 so that the coated surface and the second metal layer 15 face each other, and heat-treating the bonding layer 14. It is composed of a silver film (silver powder sintered body) formed of.

The thickness of the bonding layer 14 is not particularly limited as long as it can bond the substrate 12 and the object to be bonded 16. Specifically, for example, it may be 1 to 100 μm.

The second metal layer 15 is a bonding layer 14 and is laminated adjacent to the opposite side of the first metal layer 13. The bonding layer 14 and the object to be bonded 16 are bonded via the second metal layer 15.
As the material of the second metal layer 15, the same material as that used for the first metal layer 13 can be used.

The object 16 is a second metal layer 15 and is laminated adjacent to the opposite side of the bonding layer 14. The object to be joined 16 is not particularly limited, and specific examples thereof include a silicon (Si) chip and a silicon carbide (SiC). Further, in the method for producing the bonded body 11 of the present embodiment, since the paste-like silver powder composition described above is used, a heat-sensitive material can also be used as the bonded object 16.

In the bonded body 11 of the present embodiment, the substrate 12 and the object to be joined 16 are bonded by the bonding layer 14. Since the bonding layer 14 is formed by using the paste-like silver powder composition described above, the bonding layer 14 has a high share strength. The shear strength of the bonded body 11 of the present embodiment is preferably 10 MPa or more, more preferably 30 MPa or more. The shear strength can be measured using, for example, a commercially available bonding tester (for example, manufactured by RHESCA). The thermal conductivity of the bonding layer 14 is preferably 75 W / mK or more, and more preferably 150 W / mK or more. The thermal conductivity can be calculated from the specific resistance of the bonding layer 14 by using the Wiedemann-Franz law.

Next, the method for manufacturing the above-mentioned bonded body 11 will be described.
The method for manufacturing the bonded body 11 of the present embodiment includes a laminating step and a sintering step.

(Laminating process)
First, the substrate 12 (first member) and the object to be joined 16 (second member) are laminated via the above-mentioned paste-like silver powder composition to form a laminated body.
Specifically, the first metal layer 13 is formed by laminating a metal on the surface of the substrate 12 by a well-known method. Similarly, a second metal layer 15 is formed on the surface of the object 16 to be joined. The method for forming the metal on the surfaces of the substrate 12 and the object to be joined 16 is not particularly limited, and specific examples thereof include a vacuum vapor deposition method, a sputtering method, a plating method, and a printing method.

Next, the above-mentioned paste-like silver powder composition is applied to the surface of the first metal layer 13 by a well-known method. The method of applying the paste-like silver powder composition to the surface of the first metal layer 13 is not particularly limited, but specifically, for example, a spin coating method, a metal mask method, a spray coating method, a dispenser coating method, or a knife. Examples thereof include a coating method, a slit coating method, an inkjet coating method, a screen printing method, an offset printing method, and a die coating method.
Next, the object to be joined 16 is placed on the paste-like silver powder composition applied to the surface of the first metal layer 13 so that the second metal layer 15 side faces each other to prepare a laminate.

(Sintering process)
Next, the laminate formed as described above is heated to dry and sinter the paste-like silver powder composition to form the bonded layer 14. The first metal layer 13 and the second metal layer 15 are joined via the joining layer 14.

The heating temperature during the heat treatment is generally 130 ° C. or higher, preferably 150 ° C. or higher. By heating at this temperature, it is possible to form a dense silver film having high heat dissipation and bondability. The upper limit of the heating temperature is not particularly limited, but may be, for example, 250 ° C. or lower, particularly 200 ° C. or lower.

The heating time during the heat treatment is preferably, for example, 30 minutes or more. When the heating time is 30 minutes or more, the shear strength of the bonding layer 14 can be increased.
The bonded body 11 is manufactured by the above steps.

As described above, the method for producing a bonded body of the present embodiment uses the above-mentioned paste-like silver powder composition as a bonding material for forming a bonding layer, and therefore, a bonded body having high heat dissipation and bonding properties by heating at a relatively low temperature. Can be manufactured.

<Silver film manufacturing method>
Next, the method for producing the silver film of the present embodiment will be described.
The silver film obtained by the production method of the present embodiment is used, for example, as an electrode of a solar cell element.
The method for producing a silver film of the present embodiment includes a coating step and a sintering step.

(Applying process)
First, the above-mentioned paste-like silver powder composition is applied to a base material.
The base material is selected from any of silicon, glass, ceramics containing a transparent conductive material, a substrate made of a polymer material or a metal, or a group consisting of ceramics including silicon, glass and a transparent conductive material, a polymer material and a metal. It can be two or more kinds of laminated bodies. Further, the base material is preferably either a solar cell element or a solar cell element with a transparent metal film. Examples of the transparent metal film include indium tin oxide (ITO), antimony tin oxide (ATO), nesa (tin oxide SnO ₂ ), IZO (Indium Zinc Oxide), and AZO (aluminum-doped ZnO). ) Etc. can be mentioned. The paste-like silver powder composition is preferably applied to the surface of the photoelectric conversion semiconductor layer of the solar cell element or the surface of the transparent metal film of the solar cell element with a transparent metal film.

(Sintering process)
Next, the base material coated with the paste-like silver powder composition is heated to dry and sintered the paste-like silver powder composition to form a silver film. The heating temperature is generally 130 ° C. or higher, preferably 150 ° C. or higher. By heating at this temperature, it is possible to form a dense silver film having high heat dissipation. The heating time is generally in the range of 10 minutes to 1 hour, preferably in the range of 15-40 minutes. The heating atmosphere is not particularly limited, and can be arbitrarily set in an atmospheric atmosphere, a vacuum atmosphere, a reducing gas atmosphere, or the like. The thickness of the silver film produced by the production method of the present embodiment is generally in the range of 0.1 μm or more and 2.0 μm or less, preferably in the range of 0.3 μm or more and 1.5 μm or less. If the film thickness is too thin, the surface resistance value may be insufficient, for example, when used as an electrode of a solar cell element. On the other hand, if the film thickness becomes too thick, the amount of silver powder used increases and the cost increases.

According to the method for producing a silver film of the present embodiment, as described above, since the above-mentioned paste-like silver powder composition is used as the material of the silver film, it is possible to produce a dense silver film by heating at a relatively low temperature. It becomes.

<Manufacturing of silver powder>
(Category I)
900 g of silver nitrate aqueous solution (silver nitrate concentration: 66% by mass) as a silver salt aqueous solution, 600 g of glucolic acid aqueous solution (glucoric acid concentration: 56% by mass) as a carboxylate aqueous solution, and hydrazine aqueous solution (hydrazine concentration) as a reducing agent aqueous solution. : 58% by mass) and 1200 g of ion-exchanged water were prepared. The prepared silver nitrate aqueous solution, glucolic acid aqueous solution and ion-exchanged water were each placed in a glass container and kept warm at 50 ° C. in a hot water bath. The prepared hydrazine aqueous solution was placed in a glass container and kept warm at 20 ° C. by a water bath.

First, while stirring the ion-exchanged water kept at 50 ° C., a silver nitrate aqueous solution kept at 50 ° C. and a glucolic acid aqueous solution kept at 50 ° C. are added to the ion-exchanged water using a tube pump. The whole amount was added dropwise over 5 minutes to generate silver nitrate particles to prepare a silver nitrate slurry. The prepared silver glycolate slurry was cooled to a temperature of 20 ° C. by air cooling.

Next, with the silver glucolate slurry kept at 20 ° C. in a water bath, the entire amount of the hydrazine aqueous solution kept at 20 ° C. was added dropwise to the silver glucholate slurry over 30 minutes using a tube pump while stirring. To prepare a mixed slurry.
Next, while stirring the prepared mixed slurry, the temperature was raised to 92 ° C. at a heating rate of 15 ° C./hour using a rubber heater, and the temperature was maintained at 92 ° C. (maximum temperature) for 0.33 hours. The heat treatment was performed to reduce the silver glukolate particles to generate silver particles to obtain a silver powder slurry. The obtained silver powder slurry was cooled to a temperature of 30 ° C. over 15 minutes in a water bath. Next, the silver powder slurry was placed in a centrifuge and centrifuged at a rotation speed of 1000 rpm for 10 minutes. The supernatant liquid (liquid layer) was removed, the remaining solid content (silver powder) was washed with water, and then dried by a freeze-drying method for 30 hours to recover the silver powder. The recovered silver powder was designated as Class I silver powder.

(Category II)
Classification II silver powder was obtained in the same manner as in Category I, except that an aqueous solution of formic acid (concentration of formic acid: 58% by mass) was used as the aqueous solution of the reducing agent.

(Category III)
Classified in the same manner as in Category I, except that an aqueous solution of ammonium formate (concentration of citric acid: 56% by mass) was used as the aqueous solution of carboxylic acids and an aqueous solution of ammonium formate (concentration of fornic acid: 58% by mass) was used as the aqueous solution of the reducing agent. Obtained III silver powder.

(Category IV)
Similar to Category I, except that an aqueous solution of malonic acid (concentration of malonic acid: 56% by mass) was used as the aqueous solution of carboxylic acids and an aqueous solution of sodium ascorbic acid (concentration of ascorbic acid: 58% by mass) was used as the aqueous solution of the reducing agent. Classification IV silver powder was obtained.

(Category V)
Classified in the same manner as in Category I, except that an aqueous solution of sodium citrate (concentration of citric acid: 56% by mass) was used as an aqueous solution of carboxylic acids and an aqueous solution of ammonium formate (concentration of fornic acid: 58% by mass) was used as a reducing agent aqueous solution. V silver powder was obtained.

(Category VI)
The silver powder of classification VI was prepared in the same manner as in classification I except that the mixed slurry was heated to a temperature of 95 ° C. and kept at 95 ° C. (maximum temperature) for 0.5 hours to obtain a silver powder slurry. Obtained.

(Category VII)
A classification VII silver powder was obtained in the same manner as in classification I, except that the mixed slurry was heated at a temperature of 92 ° C. (maximum temperature) for 0.25 hours to obtain a silver powder slurry.

(Category VIII)
The silver powder of classification VI was prepared in the same manner as in classification I except that the mixed slurry was heated to a temperature of 70 ° C. and kept at 70 ° C. (maximum temperature) for 0.5 hours to obtain a silver powder slurry. Obtained.

(Category IX)
A classification VI silver powder was obtained in the same manner as in classification I, except that the mixed slurry was heated to a temperature of 97 ° C. and kept at 97 ° C. (maximum temperature) for 1 hour to obtain a silver powder slurry. ..

<Evaluation of silver powder>
The average particle size of the silver powder produced in the classifications I to IX and the detected amounts of C ₃ H ₃ O ₃ ⁻ ions and C ₆ H ₆ O ₈ ^{− ions with respect to Ag +} ions were measured by the following methods.

(Measuring method of average particle size)
The silver powder was mixed with an epoxy resin, and the obtained mixture was cured to prepare a sample for measuring the average particle size. The central portion of the sample for measuring the average particle size was cut, and the cut surface was polished with an argon ion beam. The polished surface is observed with a SEM (scanning electron microscope), 1000 or more silver particles are randomly selected, and the diameter of the selected silver particles in the direction along the irradiation direction of the argon ion beam is determined. It was measured as a particle size, and the average of the measured particle sizes was calculated.

(Ag _C 3 _H 3 against ⁺ ions _{O 3} ^- ions and _C 6 _H 6 _{O 8} ^- method of measuring the detected amount of ions)
Ag ⁺ _{C 3 H} 3 _O 3 on ion ^- ion and _C 6 _H 6 _{O 8} ^- Detection of ions were measured from time-of-flight secondary ion mass spectrometry (TOF-SIMS). A sample in which silver powder was embedded in the surface of the In foil was used as a measurement sample. The measuring device used was nanoTOFII manufactured by ULVAC-PHI. The measurement range was 100 μm square, the primary ion was Bi ₃ ⁺⁺ (30 kV), and the measurement time was 5 minutes to obtain a TOF-SIMS spectrum. From the obtained TOF-SIMS spectrum, the amount of Ag ⁺ ion, C ₃ H ₃ O ₃ ⁻ ion, and C ₆ H ₆ O ₈ ⁻ ion detected was determined, and C ₃ H ₃ O ₃ ⁻ ion and C ₆ H ₆ O were obtained. ₈ ^- a detectable amount of ions, each divided by the detected amount of Ag ⁺ ions, _C 3 _H 3 for Ag ⁺ ions _{O 3} ^- ions and _C 6 _H 6 _{O 8} ^- to calculate the detected amount of ions.

The results of each measurement are shown in Table 1 below. Table 1 also shows the types of silver salts, carboxylates and reducing agents used in the production of silver powder, and the heat treatment conditions (maximum temperature, holding time) of the mixed slurry.

<Manufacturing of paste-like silver powder composition>
[Example 1 of the present invention]
Class I silver powder as silver powder, amine-based polymer dispersant as a dispersant (peak top molecular weight measured by gel filtration chromatography (Tosoh, LC-8020): 8000), and butyl carbitol acetate as a solvent. Weighed so that the blending amount of each was 87: 3:10 by mass, and placed in a container. Next, using a kneader (manufactured by THINKY, "Awatori Kentarou"), this container is rotated at a rotation speed of 2000 rpm for 5 minutes three times to knead the silver powder, the dispersant, and the solvent. To produce a paste-like silver powder composition.

[Examples 2 to 11 of the present invention and Comparative Examples 1 to 9]
A paste-like silver powder composition was produced in the same manner as in Example 1 of the present invention, except that the types of silver powder, dispersant, and solvent shown in Table 2 were weighed and used in the blending amounts shown in Table 2. did.

<Evaluation of paste-like silver powder composition>
The coatability of the paste-like silver powder compositions produced in Examples 1 to 11 of the present invention and Comparative Examples 1 to 9 was evaluated. Further, the heat dissipation and the bondability of the silver film (bonding layer) prepared by using the paste-like silver powder composition were evaluated. Finally, a comprehensive evaluation was conducted. The results are shown in Table 3.

(Evaluation of coatability)
The coatability was evaluated from the viscosity of the paste-like silver powder composition.
The viscosity of the paste-like silver powder composition was measured using a rheometer. The measurement temperature was 25 ° C., and a jig having a diameter of 20 mmφ was used to measure the viscosity when the shear rate was 10 [/ s].

As for the coatability, those having a viscosity measured by the above method of 15 Pa · s or more and 40 Pa · s or less are marked with ⊚, and those having a viscosity of 10 Pa · s or more and less than 15 Pa · s or more than 40 Pa · s and 50 Pa · s or less are marked with ◯. , Those exceeding 50 Pa · s were marked with x.

(Evaluation of heat dissipation)
A paste-like silver powder composition was applied onto a glass substrate using a metal mask plate (hole size: length 10 mm × width 10 mm, thickness: 50 μm) to form a coating film. Next, the coating film was heated in an atmospheric atmosphere of 200 ° C. for 60 minutes in a muffle furnace to prepare a silver film on a glass substrate. Then, the thermal conductivity of the produced silver film was measured.

The thermal conductivity was calculated using the Wiedemann-Franz law. That is, the sheet resistance value and the film thickness of the silver film were measured in an environment of a temperature of 25 ° C. (absolute temperature T = 298K). Then, the specific resistance σ (= sheet resistance value × film thickness) of the silver film was obtained, and the thermal conductivity K (unit: W / mK) was calculated by the following formula.
K = L × T × σ
(L: Lorentz number L = 2.44 × ^10-8 WΩK- ² , T: temperature = 298K)

Regarding the heat dissipation, those having a thermal conductivity of 150 W / mK or more measured by the above method were evaluated as ⊚, those having a thermal conductivity of 75 W / mK or more and less than 150 W / mK were evaluated as ◯, and those having a thermal conductivity of less than 75 W / mK were evaluated as x. Those in which a coating film having a uniform thickness could not be formed on the glass substrate were not evaluated.

(Evaluation of bondability)
An aluminum substrate whose surface is coated with a silver layer and a silicon chip whose surface is coated with a silver layer (bottom surface: length 2.5 mm × width 2.5 mm, thickness: 200 μm) were prepared. The paste-like silver powder composition was applied to the surface (silver layer) of the aluminum substrate using a metal mask plate (hole size: length 3 mm × width 3 mm, thickness: 50 μm) to form a coating layer. Next, the bottom surface of the silicon chip is placed on the coating layer, and the coating layer is sintered by heating at a temperature of 200 ° C. for 60 minutes in the atmospheric atmosphere to form a bonding layer between the aluminum substrate and the silicon chip. Obtained a sinter. Then, the shear strength of the joint layer of the obtained joint was measured.

For the shear strength, the force required to break the bonding layer formed between the aluminum substrate and the silicon chip is measured by a bonding tester (manufactured by RHESCA), and this measured value is measured as the bonding area (the area of the bottom surface of the silicon chip). ) To give the share strength.

Regarding the bondability, those having a shear strength of 30 MPa or more measured by the above method were evaluated as ⊚, those having a shear strength of 10 MPa or more and less than 30 MPa were evaluated as ◯, and those having a shear strength of less than 10 MPa were evaluated as x. Those in which a coating layer having a uniform thickness could not be formed on the surface of the aluminum substrate were not evaluated.

(Comprehensive evaluation)
Those with all three evaluation items of coatability, heat dissipation and heat dissipation being ◎ were marked with ◎, and one or two of the three evaluation items were ◎ and the rest were ○. When all three evaluation items were ○, it was evaluated as Δ, and when even one of the three evaluation items had ×, it was evaluated as ×.

In Comparative Example 1, heat dissipation and bondability were low. This is because the amount of organic matter covering the surface of the silver particles has become too large, so that during the heating of the silver film production, the sintering between the silver particles and between the silver particles and the object to be bonded is suppressed, and silver. It is considered that this is because the density of the film has decreased. In Comparative Example 2, the coatability was low, and the heat dissipation and bondability could not be evaluated. It is considered that this is because the amount of organic matter covering the surface of the silver particles is too small, resulting in poor adsorption of the polymer dispersant on the surface of the silver particles. In Comparative Example 3, the coatability was low, and the heat dissipation and bondability could not be evaluated. It is considered that this is because the effect of suppressing the aggregation of silver particles is weakened by using low molecular weight butylamine as the dispersant. In Comparative Example 4, heat dissipation and bondability were low. This is because the molecular weight of the polymer dispersant has become too large, so that it is difficult for the silver particles to separate from the surface of the silver particles during heating during the production of the silver film, and the silver particles and between the silver particles and the object to be bonded are sintered. It is considered that this is because the density of the silver film is reduced due to the suppression of the silver film. In Comparative Example 5, it is considered that the effect of the polymer dispersant could not be obtained because the content of the polymer dispersant was too small. In Comparative Example 6, heat dissipation and bondability were low. This is because the content of the polymer dispersant was too large, so the amount of the polymer dispersant remaining on the surface of the silver particles during heating during the production of the silver film increased, and the silver particles and the silver particles to be bonded to each other. It is considered that this is because the sintering with the silver film was suppressed and the density of the silver film decreased.

In Comparative Example 7, heat dissipation and bondability were low. This is because the polymer dispersant has a carboxyl group, and this carboxyl group strongly adheres to the silver particles, and the amount of the polymer dispersant remaining on the surface of the silver particles during heating during the production of the silver film is large. It is considered that this is because the sintering between the silver particles and between the silver particles and the object to be joined was suppressed, and the density of the silver film decreased. In Comparative Example 8, the coatability, heat dissipation, and bondability were low. It is considered that the reason why the coatability was lowered was that the molecular weight of the polymer dispersant became too small and the effect of suppressing the aggregation of silver particles was weakened. In addition, the heat dissipation and bondability were lowered because the polymer dispersant had thio groups, and these thio groups strongly adhered to the silver particles, and the surface of the silver particles was heated during the production of the silver film. It is considered that this is because the amount of the polymer dispersant remaining in the silver particles increased, the sintering between the silver particles and between the silver particles and the object to be bonded was suppressed, and the density of the silver film decreased. Comparative Example 9 had poor coatability. It is considered that this is because the dispersion effect is suppressed because the compatibility between the solvent and the polymer dispersant is low.

On the other hand, the paste-like silver powder compositions of Examples 1 to 11 of the present invention had excellent coatability, and the silver film obtained by heating at 200 ° C. had high heat dissipation and bondability.
From the above results, according to the example of the present invention, a paste-like silver powder composition having excellent coatability and capable of forming a silver film (silver powder sintered body) having high heat dissipation and bondability by heating at a relatively low temperature can be obtained. It was confirmed that it would be possible to provide it. Further, according to the example of the present invention, a method for producing a bonded body capable of producing a bonded body having high thermal conductivity and bonding strength by heating at a relatively low temperature and high thermal conductivity by heating at a relatively low temperature. It was confirmed that it becomes possible to provide a method for producing a silver film capable of producing a silver film.

11 ... Bonded body 12 ... Substrate 13 ... First metal layer 14 ... Bonded layer 15 ... Second metal layer 16 ... Jointed object 17, 18 ... Interface

Claims (4)

It contains silver powder, a polymer dispersant having an amino group or a phosphate group , and at least one solvent selected from the group consisting of diols and carbitol acetates.
The silver powder is selected from the group consisting of one or more carboxylic acids selected from the group consisting of glycolic acid, ammonium citrate and malonic acid or salts thereof, and hydrazine, formic acid, ammonium formate and sodium ascorbate. one or organic compounds derived from the two or more reducing agents are adhered to the surface, as measured by time-of-flight secondary ion mass spectrometry, C ₃ H ₃ O ₃ derived from the organic compound ^- detection of ions is, the detection of Ag ⁺ ions, 0. In the range of 1.0 times more than doubled, and the C ₆ H ₆ O ₈ derived from organic compounds ^- detecting the amount of ions, the detection amount of the Ag ⁺ ion, 0.005 times 0 It is in the range of .02 times or less,
The polymer dispersant has a peak top molecular weight in the range of 1500 or more and 15000 or less as measured by gel filtration chromatography.
A paste-like silver powder composition, wherein the content of the polymer dispersant is in the range of 1% by mass or more and 5% by mass or less. The paste-like silver powder composition according to claim 1, wherein the solvent is ethylene glycol, 2-ethyl-1,3-hexanediol or butylcarbitol acetate. A method for manufacturing a bonded body in which a first member and a second member are joined via a bonding layer.
A laminating step of forming a laminated body in which the first member and the second member are laminated via the paste-like silver powder composition according to claim 1 or 2.
A sintering step of heating the laminate to dry and sintered the paste-like silver powder composition to form a bonded layer.
A method for producing a bonded body, which comprises. A coating step of applying the paste-like silver powder composition according to claim 1 or 2 to a base material, and
A sintering step of heating a base material coated with the paste-like silver powder composition to dry and sintered the paste-like silver powder composition to form a silver film.
A method for producing a silver film, which comprises.

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